An ion implanter includes an ion source for converting a gas or a solid material into a well-defined ion beam. The ion beam typically is mass analyzed to eliminate undesired ion species, accelerated to a desired energy, and implanted into a target. The ion beam may be distributed over the target area by electrostatic or magnetic beam scanning, by target movement, or by a combination of beam scanning and target movement. The ion beam may be a spot beam or a ribbon beam having a long dimension and a short dimension.
Implantation of an ion species may allow a substrate to be cleaved. The species forms microbubbles in the substrate material. These microbubbles are pockets of a gas or regions of an implanted species below the surface of the substrate that may be arranged to form a weakened layer or porous layer in the substrate. A later process, such as heat, fluid, chemical, or mechanical force, is used to separate the substrate into two layers along the weakened layer or porous layer.
Ostwald ripening may occur in substrates that have microbubbles. Ostwald ripening is a thermodynamic process where larger particles grow by drawing material from smaller particles because larger particles are more stable than smaller particles. Any atoms or molecules on the outside of a particle, which may be, for example, a microbubble, are energetically less stable than the more ordered atoms or molecules in the interior of a particle.
This is partly because any atom or molecule on the surface of a particle is not bonded to the maximum possible number of neighboring atoms or molecules, and, therefore, is at a higher energy state than those atoms or molecules in the interior. The unsatisfied bonds of these surface atoms or molecules give rise to surface energy. A larger particle, with a greater volume-to-surface ratio, will have a lower surface energy. To lower surface energy, atoms or molecules on the surface of smaller, less stable particles will diffuse and add to the surface of the larger, more stable particles. The shrinking of smaller particles will minimize total surface area and, therefore, surface energy. Thus, smaller particles continue to shrink and larger molecules continue to grow.
FIG. 1 is a view of Ostwald ripening in a substrate. FIG. 1 is merely an illustration and is not to scale. A species that forms the microbubbles 100 in the substrate 138 makes smaller microbubbles 101 and larger microbubbles 102. Due to their greater volume-to-surface ratio and lower surface energy, the larger microbubbles 102 will be more stable than the smaller microbubbles 101. To lower their surface energy, the smaller microbubbles 101 will diffuse to the larger microbubbles 102 (as illustrated by the dotted lines in FIG. 1). Overall, the smaller microbubbles 101 may shrink and the larger microbubbles 102 may grow. Some of the species in the microbubbles 100 also may diffuse out of the substrate 138 altogether. Ostwald ripening and diffusion of the species out of the substrate 138 will affect the substrate 138 when it is cleaved along the weakened layer or porous layer represented by the dashed line 103.
Previous methods have implanted hydrogen or a combination of hydrogen and helium to cleave a substrate. This typically requires a dose of hydrogen of greater than approximately 2E16 cm−2, such as approximately 6E16 cm−2, or a co-implant of hydrogen and helium with a dose of approximately 1E16 cm−2 each. Such high doses during implant make this cleaving process expensive and time-consuming. Accordingly, there is a need in the art for an improved process to cleave a substrate and, more particularly, a process that will form microbubbles that are used to cleave a substrate.